This invention relates to a buffer or shock absorber for use in the suspension mechanism of a vehicle and more particularly, to a buffer for use in a vehicle suspension mechanism of the type including a double-walled cylindrical structure which includes an inner or actuation cylinder the interior of which is sealably filled with oil, and an outer cylinder which surrounds the inner cylinder in peripherally spaced relationship thereto and a portion of which is sealably filled with compressed air and another portion of which is sealably filled with liquid. In this type of buffer, it is necessary that air trapped in the actuation cylinder as the result of aeration generated while the vehicle is running or while the buffer is operating be recycled to the annular space defined between the actuation cylinder and outer cylinder. On the other hand, at the downstroke of the piston of the actuation cylinder, since the pressure within the outer cylinder increases somewhat at such a time, the air should be prevented from entering the actuation cylinder.
In order to obtain such functions, there has been proposed and practically employed a type of buffer including an inner or actuation cylinder filled with hydraulic fluid and including a piston for slidable movement within the cylinder, and a piston rod having a lower end to a piston and an upper end extending beyond the upper end of the cylinder. An outer cylinder surrounds the actuation cylinder in a peripherally spaced relationship thereto to define an annular oil reservoir therebetween. The reservoir has an opening at the lower end thereof in communication with the lower end of the actuation cylinder. The upper portion of the outer cylinder is filled with air under pressure and includes means which allows the hydraulic fluid in communication with the upper end of the actuation cylinder to enter the oil reservoir, but which prevents the fluid from flowing from the oil reservoir to the actuation cylinder.
Furthermore, an improvement of the above-mentioned buffer has been proposed and practically employed in a buffer. The improvement includes a seal at the upper end of the actuation cylinder through which the piston rod extends, a recess defined between a piston rod guide and a seal support in communication with the upper end of the oil reservoir, one or more passages defined between the piston rod and seal and extending inwardly toward the recess in communication with the upper portion of the actuation cylinder, and a resilient valve member received within the recess. The valve member is adapted to resiliently deform to close the end or ends of the associated passage or passages so as to provide a flow of fluid in one direction when any excessive pressure is present in the cylinder.
In any one of the above-mentioned prior art buffers, there is provided one of various one-way valves in the narrow passage which communicates between the actuation cylinder and outer cylinder. However, such one-way valves have disadvantages in that the valves can not be easily mounted in the narrow passage and that the valves are complicated in construction and, accordingly, are expensive. Furthermore, since the seal is designed to withstand a high pressure produced by the damping action produced during the operation of the buffer, such a seal inevitably has a complicated construction, and the seal has a very short service life.